#include<cstdio>#include<cstring>#include<cstdlib>#include<cmath>#include<algorithm>#include<string>#include<map>#include<set>#include<iostream>#include<vector>#include<queue>using namespace std;#define sz(v) ((int)(v).size())#define rep(i, n) for (int i = 0; i < (n); ++i)#define repf(i, a, b) for (int i = (a); i <= (b); ++i)#define repd(i, a, b) for (int i = (a); i >= (b); --i)#define clr(x) memset(x,0,sizeof(x))#define clrs( x , y ) memset(x,y,sizeof(x))#define out(x) printf(#x" %dn", x)#define sqr(x) ((x) * (x))typedef long long lint;const int maxint = -1u>>1;const double eps = 1e-8;int sgn(const double &x) { return (x > eps) - (x < -eps); }const int maxn = 1000 + 10;const int maxm = 20000 + 10;map<int, int> mp[maxn];int n, m;vector<int> e[maxn], g[maxn];int t[maxm];queue<int> que;void add(vector<int> *e, int x, int y) { e[x].push_back(y);}vector<int> getTop(vector<int> *e) { vector<int> res; int in[maxn] = {0}; repf (i, 1, n) rep (j, sz(e[i])) in[e[i][j]]++; repf (i, 1, n) if (in[i] == 0) que.push(i); while (!que.empty()) { int k = que.front(); que.pop(); res.push_back(k); rep (i, sz(e[k])) { int j = e[k][i]; in[j]--; if (in[j] == 0) que.push(j); } } return res;}vector<int> ans;int getAns(vector<int> &se, vector<int> &sg) { int pos[maxn], v[maxn] = {0}, down[maxn] = {0}; ans.clear(); rep (i, sz(sg)) { pos[sg[i]] = i; } rep (i, sz(se)) { int k = -1; rep (j, sz(se)) { if (v[se[j]]) continue; if (k == -1 || pos[se[k]] > pos[se[j]]) k = j; } int w = se[k]; repd (j, k - 1, pos[w]) { if (mp[se[j]].count(w)) { int h = mp[se[j]][w]; if (t[h]) return false; else ans.push_back(h); } swap(se[j], se[j + 1]); } v[w] = 1; } return true;}int main() { while (scanf("%d%d", &n, &m) == 2) { clr(t); repf (i, 1, n) { e[i].clear(); g[i].clear(); mp[i].clear(); } repf (i, 1, m) { int x, y, ty; scanf("%d%d%d", &x, &y, &ty); if (mp[x][y] != 0) { t[mp[x][y]] = 1; t[i] = 1; } mp[x][y] = i; add(e, x, y); if (ty == 0) add(g, x, y); else add(g, y, x); } vector<int> se = getTop(e); vector<int> sg = getTop(g); if (!getAns(se, sg)) printf("-1n"); else { printf("%dn", sz(ans)); rep (i, sz(ans)) { if (i) printf(" "); printf("%d", ans[i]); } if (sz(ans)) puts(""); } printf("n"); } return 0;}
